New guidance for internal shading as temperatures rise

TM69 recognises that shading systems, such as internal blinds, simultaneously affect internal daylight and acoustic conditions, as well as the thermal and solar performance of a building.

CIBSE’s new technical memorandum Dynamic thermal modelling of basic blinds (TM69:2022) recognises the role of internal shading in reducing indoor air temperatures, as well as the impact on internal daylight and acoustics.

The UK has recently experienced air temperatures in excess of 40°C, smashing previous records. The new guide highlights some of the issues associated with the discrepancies between blind performance in a model and in a real-life application. Future software applications will need to align with the relevant standards.

TM69 recognises that shading systems, such as internal blinds, simultaneously affect internal daylight and acoustic conditions, as well as the thermal and solar performance of a building.

It also examines some of the limitations that are present when including moveable blinds in a dynamic thermal model.

The guide’s focus is on representing a more straightforward approach, in thermal analysis terms, to glass-blind systems in some typical software packages. It also suggests ‘workarounds’ for better representations.

Although Approved Document O:Overheating for newly developed residential buildings only accepts external shading as a measure to mitigate solar gains, the content of TM69 is helpful in giving background to the combined physics of glass-blind systems, recognising the differences between external and internal blind elements.

The development of TM69 was led by the CIBSE Building Simulation Group.
● Copies of TM69:2022 are available from the CIBSE Knowledge Portal at www.cibse.org/knowledge